Safety stop device



Sept. 22, 1953 A. c. CHRISTENSEN SAFETY STOP DEVICE 2 Sheets-Sheet 1 Filed Aug. 19, 1949 Patented Sept. 22, 1953 SAFETY STOP DEVICE Alfred C. Christensen; Chicago, 111., assignor, by

mesne assignments, to Herbert Simpson Corporation, Chicago, 111., a corporation of Illinois Application August 19, 1949, Serial N 0. 111,158

straight line or at an angle to each other, .the

shut-down of a forward unit due to an operational defect will result in material being piled on this unit by rearward units which feed material thereto until the breakdown is discovered and all units are stopped. 11f the-conveyorsystem ina remote or hidden position, this breakdown may not be discovered for a considerable time. In the foundry industry, such a failur in a sand carrying conveyor system causes large quantities of sand to be piled onto the idle conveyor. Much time is spent in clearing away the sand before the system can be returned to operation and in the meantime all the foundrymen are idle. Thus, such a breakdown causes considerable loss of time.

According to the teachings of the present invention, the electric drive mechanism of :each separately driven conveyor unitiis interconnected with the drive means of the unit to which it delivers material. each unit is equipped with a pin which will be sheared when the apron or conveying surface of the conveyor is stopped due to a breakdown or a jamming of material. After the shear pin break the drive :gear continues to rotate and thereby releases a spring arm which contacts a switch to deenergize the drive motor and simultaneous'ly energize a visible and an audible warning signal. Since the drive motor for the second conveyor unit is interconnected in the electric circuit of the drive means of the first conveyor unit, it will also be deenergized. Thus, piling up of=materia1 will be avoided.

It is thereforean important object of the present invention to provide means for automatically shutting down rearward conveyor units when a forward conveyor unit is stopped due to an operational defect.

Another object of this invention is to provide an automatic safety stop device for a series of conveyor units which is directly connected to the driving mechanism of one of the conveyors and arranged for immediate operation as soon as a breakdownoccurs.

A further object of this invention is to pro- The driv gear 'or sprocket of vide an automatic safety stop device which is arranged to energize audible and visible warn- .ing signals when a breakdown occurs and to continue the energization of these warning signals until they are purposely shutoff by a workman.

An important feature of this invention is the provision of .a novelsafety catch and spring arm, the mechanism :of which, upon the stopping of the-conveyon'will permit the safety arm to spring out .into position to contact a control switch for deenergizing the drive means of a following-coniveyor uni-t.

Another feature of this invention is the provision of a novel interlocking control circuit for a series of conveyor units.

Other and further features, objects and advantages of the present invention will be apparent to one skilled in the art from the following detailed description takenin connection with the accompanying drawings.

:On the drawings:

Figure 1 is a fragmentary top plan view of two conveyor units having an automatic safety stop :device constructed according to the teachings of the present invention.

Figure 2 is a fragmentary enlarged side'elevational view taken along line IIII 01 Figure 1 with the cover of the gear housing removed to show the safety stop device of this invention.

Figure 3 is an enlarged fragmentary horizontal sectional view taken on line 111-111 of Figure 2, with partsin elevation.

Figure 4 is a diagrammatic electrical control circuit adapted for use in the present invention.

As shown on :the drawings:

In Figure 1 the reference numeral it indicates a conveyor unit including a conveying surface ll disposed in driving engagement with a chain 12, through any suitable connection, as by arms I 3 which are secured to the side face of the chain and to the surface H. The chain I2 is disposed around sprocket wheels is which are keyed to a drive shaft l8 journaled in bearings iii of a frame support structure is. It will be understood of course that any type of conveyor unit may be used in this invention so long as it has a drive shaftsimilar-to drive shaft it.

A driven gear 2| is mounted on the drive shaft I6 and is'in mesh with a pinion gear 22, which is operatively connected in a manner to be described hereinafter, to a drive shaft 24 of a motor '25. The drive shaft 24 is journaled for rotation in bearings ill in the opposite side walls of the frame structure it. Thus, when the motor 25 is energized, the conveyor surface it 3 will be moved due to its driving connection through the drive shaft 24.

Power is transmitted from the gear 2| to the shaft l6 through a shear pin 38 (Figures 2 and 3), which is tightly disposed in an aperture 32 of the gear 2| and in an aperture 33 of a hub member 34. The shaft |6 passes freely through a central opening 36 in the gear 2| and is secured, as by a square key 31, in an opening 38 in the hub 34.

The safety trip device of this invention comprises a spring arm 48 (Figure 2) which is secured by bolts 4| to a projecting ledge 42 of an angle bracket 43 secured to the web portion of the gear 2|. The spring arm 40 has an arcuate configuration with a free end portion 40a adapted to be held behind the projecting end 45a of a bent keeper arm 45. This arm 45 is secured at one end by bolts 46 to the hub 34.

If material becomes jammed on the conveyor surface causing the conveyor surface to be stopped, the drive shaft I6, which is directly connected to this surface through the chain l2 and arms I3, will of course also be stopped. This will cause the shear pin 33 to be sheared since the gear 2| will continue to rotate due to its positive drive connection with the driving motor 25. Referring to Figure 2, it will be seen that, when the gear 2| continues to rotate in a clockwise direction while the hub 34 remains stationary due to the jamming of the conveyor surface, the bracket 43 will be carried around and there will be relative separating movement between the end 40a of the spring arm 48 and the end 45a of the keeper 45. When these two members disengage, the spring arm 40 will spring outwardly to the dotted line position illustrated in Figure 2. Upon further rotation of the gear 2|, the spring arm end 4801. will contact a roller 41a (Figure 2) on the end of a lever arm 41b, which is arranged to shift the contacts of a single pole, double throw microswitch 41, which serves as shutdown, or safety switch. Said micro-switch 41 is mounted on the inner face of the housing 48 for the gear 2| and is so arranged that the roller 4111 will be in the path of travel of the end 46a of the spring arm 40. A cover 48a (Figure 1) normally closes the gear housing 48.

A second conveyor 49 (Figure l) is mounted directly behind the conveyor unit l6 having a delivery portion 49a arranged to direct material onto the conveyor unit I8. Said second conveyor 49 is driven by an electric motor 50.

Electric control circuit In Figure 4 the letters A, B and C indicate three conductor leads from a three phase source of electric power. The switch 41 is the single pole, double throw micro-switch, previously referred to as being mounted on the gear housing 48, while the numerals and 52 indicate, respectively, an audible alarm and a visible alarm.

In operation, the switch 41 is normally closed as indicated in Figure 4, thereby connecting conductors 54 and 55. A single throw three-bladed switch 56 is provided to connect the conductors leading from the lines A, B and C to conductors 58, 59 and 60, respectively. When the switch 56 is closed, a solenoid 62 will be energized after a normally open push button switch 63 is closed. The circuit is then established from conductor A through the switch 56, conductor 58, conductor 65, solenoid 62, a normally closed switch 66, conductor 61, switch 63, conductor 68, conductor 55,

4 switch 41, conductor 54, and conductor 69 to the line C.

When the solenoid 62 is energized, it draws a plunger 10 of magnetic material to the left as shown in Figure 4 causing an insulating bar 12 to move to the left carrying cross conductors 13, 14, 15 and 16 therewith. The cross conductors 13, 14 and 15 connect the conductors '58, 59 and 68 to leads 11, 18 and 19 of the three phase motor 25, thus energizin it to start up the conveyor.

It is also to be noted that upon energization of the solenoid 62, the cross conductor 16 connects conductors 88 and 8| to close a holding circuit for the solenoid 62. The holding circuit comprises said conductor 8| and includes the switch 66. Thus, when the push button switch 63 is released, the motor 25 will not be deenergized.

The motor 58 which drives the conveyor 49 is controlled through anidentical control circuit. A conductor 83 connects the control circuit for the motor 59 to the lead C through the control circuit of the motor 25. Since the control circuits for the conveyors 49 and H] are identical, the elements of the control circuit for the conveyor 49 will be given identical reference numerals with a suflix a affixed thereto.

Thus, when the switch 56a is closed and the push button switch 63a is closed, the solenoid 62a will be energized, causing the cross conductors 13a, 14a and 15a to energize the motor 50, and causing the cross conductor 16a to close a holding circuit for the solenoid 62a. A line 83a connects the control circuit of the conveyor 59 with any following conveyor unit control circuit.

When the safety stop spring arm 40 is released due to a stopping of the conveyor surface H and of the drive shaft I6, the single pole, double throw micro-switch 41 is actuated by the spring arm 40, as previously described. The micro-switch 41 then moves to a position connecting the conductor 54 with a conductor 85 in circuit with a solenoid 86. The circuit is completed from the line C through conductor 69, conductor 54, switch 41, conductor 65, conductor 81, solenoid 86, a normally closed switch 88, and conductor 89 to the line A.

When the solenoid 86 is energized it draws a magnetic plunger 98 upwardly, as indicated in Figure 4, to cause an insulating bar 9| carrying a cross-connector 92 to establish electrical communication through said cross-connector 92 with conductors 93 and 94. This will establish a holding circuit for the solenoid 86 and therefore when the micro-switch 41 is swung back to the position indicated in Figure 4, the solenoid will still be energized until the push button switch 88 is opened.

The energization of the solenoid 86 also causes the insulating bar 9| to move a cross-conductor 95 into contact with conductors 96 and 91. In this manner an audible alarm 5|, which may be a bell ringing alarm, and a visible alarm 52, which may be a red light, are energized. These two alarms 5| and 52 will remain energized until the push button switch 88 is opened.

While in Figure 1 the conveyor I0 is illustrated as being the only one to which a safety stop trip is connected, it will of course be understood that this safety stop device may be connected to the drive shaft of any one or all of the conveyor units. Thus it may be necessary to install such a safety device on every conveyor unit so that, in case of failure of this unit, all followin conveyor units will be automatically stopped. However, it will be noted that some conveyor units may be comparatively trouble-free due to their simple operation while other units may be in installations where jamming might easily occur.

From the foregoing description it will be seen that there is provided in this invention a simple effective spring type safety stop device which is so arranged that it will quickly and automatically shut down following conveyor units and simultaneously set off an alarm system which will remain connected until positively disconnected by a workman.

This installation is very economical in that it requires only a simple bracket device, and a simple spring arm and keeper.

It will be understood that modifications and variations may be effected without departing from the scope or the novel concept of the present invention.

I claim:

1. In a drive mechanism including a shaft, a rotary member, and a shear pin connecting said shaft to said rotary member in driving relation, a trip mechanism adapted to be released when said shear pin fails, said trip mechanism comprising a cantilever spring arm mounted on said rotary member for rotation therewith, means carried by said shaft for retaining said spring arm under tension so long as driving relation between said shaft and said rotary member i established by said shear pin, said spring arm being released by said means upon fracture of said shear pin, and control means interposed in the path of travel of said spring arm upon continued rotation of said rotary member after said shear pin has been fractured.

2. In combination, a shaft having an extending arm portion, a rotary member adjacent said arm portion having a central opening receiving said shaft freely therethrough, a shear pin drivingly connecting said shaft arm portion and said rotary member, power means for driving said rotary member, said shaft being driven through said shear pin connection to said rotary member, an electric control circuitfor said power means including a fixed switch mounted adjacent said rotary means, a keeper mounted on said extending arm portion, and a resiliently defiectible spring arm on said rotary member having an end portion normally disposed behind said keeper to be frictionally retained thereby under tension, said end portion being moved from behind said keeper and released from its deflected condition to actuate said switch and open said control circuit when said shear pin fails, thereby accommodating relative rotative movement of said rotary member and said shaft.

3. In a drive mechanism including a pair of relatively movable elements, one of which is rotatable on a shaft and the other of which is loosely mounted thereon, and a frangible shear pin securing said elements together for co-rotation; the improvements of a keeper fixedly mounted on one of said elements for rotation therewith in closely spaced relation to the other of said elements, an

elongated resiliently deflectable actuating arm carried by the other of said elements for rotation and normally retained in resiliently tensioned position by said keeper, and stationary control means positioned adjacent the other of said elements outside the path of movement of said arm when retained by said keeper and within the path of movement when said arm is released from said keeper by relative movement of said elements upon fracture of said shear pin.

4. In a conveyor drive system, a driven shaft, an arm rotatable with said shaft, a rotary driving member loosely mounted on said shaft, a shear pin connecting said shaft arm to said rotary member, a fixed housing enclosing the periphery of said driving member, control means carried by said housing and projecting inwardly therefrom toward said shaft to lie alongside said rotary means, a keeper carried by said arm and having an outturned lip, a resiliently defiectable cantilever spring arm carried by said rotary member and having one end normally underlying the lip of said keeper in frictional engagement therewith, said spring arm being resiliently tensioned inwardly toward said shaft, fracture of said shear accommodating relative movement of said keeper and said spring arm to release said spring arm for movement into alignment with said control means to actuate said control means upon continued rotation of said rotary member.

5. In a drive mechanism including a drive member, a driven member, and a shear pin connecting said drive member to said driven member for driving said driven member from said drive member, a trip mechanism releasable when said shear pin fails, said trip mechanism comprising an arm rotatable with said drive member and a keeper carried by said driven member for restraining said arm as long as driving relation between said drive member and said driven member is established by said shear pin, said arm being releasable by said keeper upon fracture of said shear pin and rotation of said arm with said drive member out of engagement with said keeper, and control means interposed in the path of travel of and actuated by said arm upon continued rotation of said arm with said drive member after said shear pin has been fractured and the arm released from said keeper.

ALFRED C. CHRISTENSEN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,340,355 Wood May 18, 1920 1,412,444 Baker Apr. 11, 1922 1,520,000 Baker Dec. 23, 1924 1,929,994 Schlotman Oct. 10, 1933 1,972,601 Regan Sept. 4, 1934 2,022,007 Moore Nov. 26, 1935 2,124,965 Lind July 26, 1938 2,205,370 Brice June 18, 1940 

